Some projection systems include light valves to modulate an incident light beam with an image signal. The light valve is also referred as an image panel. The image panel can be transmissive or reflective. The number of image panels in a projection system might be either one or three. In a three-panel projection system, a white light beam which is emitted from a white-light source is separated into red, green, and blue (RGB) color beams. The three color beams are modulated by an individual panel, and then are combined to form an image. The advantage of three-panel projection system has high optical efficiency. The weakness is higher cost and complexity, and also requires precise alignment among the three image panels. In a single-panel system, a color wheel is for filtering the white light into one of the R, G, and B color beams sequentially. Only one color beam can be transmitted onto the image panel at any one time, and the light of other two colors are discarded. The advantage of single-panel is compact and lower cost and the optical efficiency only achieves ⅓ of a three-panel system.
A color scrolling technique is then developed to increase the optical efficiency of the single-panel projection system. The white light beam is separated into R, G, and B color beams, and the three color beams are simultaneously transmitted onto different portions of the image panel. The three color beams are scrolled across the image panel, and every pixel of image panel can be illuminated by the three color beams sequentially.
A single-panel scrolling projection system is shown in FIG. 1. A white light emitted from a light source 101 passes through a condenser lens 111, and is separated into R, G, and B color beams through dichroic mirrors 102, 103, and a mirror 104. The red beam R is reflected by the dichroic mirror 102, and is then propagated through a rotating prism 108. The green beam G passes through the dichroic mirror 102 and a field lens 112, and is reflected by the dichroic mirror 103, and is then propagated through a rotating prism 109. The blue beam B passes through the dichroic mirror 102, 103 and the field lens 112, 113, and is reflected by the mirror 104, and is then propagated through a rotating prism 110. The rotating prisms 108, 109 and 110 will cause the positions of three color beams to be scrolled by refraction. The scrolling color beams are then combined through the dichroic mirrors 105, 106, and a mirror 107. The field lenses 114, 115, 116, 117, 118 are used to define the shape of the scrolling color beams. The combined beams impinge onto the surface of an image panel 120 via the relay lens 119, and are then modulated by the image panel 120. The three prisms rotate synchronously. The R, G, B color beams can keep scrolling on the image panel simultaneously. When the R, G, B color beams scroll one cycle, one frame of color image is formed.
In the conventional single-panel projection system, the scrolling speed for the color beams is not constant, and it is uneasy to synchronize the image modulation with scrolling color bands. The incident angle of color beams passed through the rotating prisms 108, 109, and 110 to the dichroic mirrors 105, 106, and 107 is not fixed, and it caused spectrum deviation of the color beams.
To overcome the foregoing shortcomings, the inventor of the present invention based on years of experience in the related field to conduct extensive researches and experiments invents a scrolling device with color separation and a projection system incorporating same to be an optimum solution.